Abstract

Direct copper electrodeposition has been of significant interest due to physical limitations of copper seed layer deposition in the dual-damascene process. A key to the successful application of direct electrodeposition onto liner materials is understanding and controlling nucleation. For example, achieving high nucleus densities is critical to obtaining coalescence thicknesses on the order of few nm. In this report, a model is presented with the aim of understanding the nucleation of copper better. The results of numerical simulations are used to explore the impact of additives on chronoamperometric behavior of the nucleation stage of electrodeposition processes, as well as their impact on particle size distributions. Because the manner in which additives affect electrodeposition processes is complex, the numerical results depend on multiple parameters. An emphasis is placed on suppressors such as polyethylene glycol used in Cu plating. The rate at which the suppressor adsorbs onto the freshly nucleated metallic particles is a key parameter in determining the time at which a current maximum is expected and the value of the peak current density. Suppressors hinder the growth of particles and also potentially lower the barrier to nucleation, resulting in a particle size distribution with smaller particles in progressive nucleation.